path: root/checker/inductive.ml

(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(* $Id: inductive.ml 10172 2007-10-04 13:02:03Z herbelin $ *)

open Util
open Names
open Univ
open Term
open Reduction
open Type_errors
open Declarations
open Environ

let inductive_of_constructor = fst
let index_of_constructor = snd
let ith_constructor_of_inductive ind i = (ind,i)

type mind_specif = mutual_inductive_body * one_inductive_body

(* raise Not_found if not an inductive type *)
let lookup_mind_specif env (kn,tyi) =
  let mib = lookup_mind kn env in
  if tyi >= Array.length mib.mind_packets then
    error "Inductive.lookup_mind_specif: invalid inductive index";
  (mib, mib.mind_packets.(tyi))

let find_rectype env c =
  let (t, l) = decompose_app (whd_betadeltaiota env c) in
  match t with
  | Ind ind -> (ind, l)
  | _ -> raise Not_found

let find_inductive env c =
  let (t, l) = decompose_app (whd_betadeltaiota env c) in
  match t with
    | Ind ind
        when (fst (lookup_mind_specif env ind)).mind_finite -> (ind, l)
    | _ -> raise Not_found

let find_coinductive env c =
  let (t, l) = decompose_app (whd_betadeltaiota env c) in
  match t with
    | Ind ind
        when not (fst (lookup_mind_specif env ind)).mind_finite -> (ind, l)
    | _ -> raise Not_found

let inductive_params (mib,_) = mib.mind_nparams

(************************************************************************)

(* Build the substitution that replaces Rels by the appropriate *)
(* inductives *)
let ind_subst mind mib =
  let ntypes = mib.mind_ntypes in
  let make_Ik k = Ind (mind,ntypes-k-1) in
  list_tabulate make_Ik ntypes

(* Instantiate inductives in constructor type *)
let constructor_instantiate mind mib c =
  let s = ind_subst mind mib in
  substl s c

let instantiate_params full t args sign =
  let fail () =
    anomaly "instantiate_params: type, ctxt and args mismatch" in
  let (rem_args, subs, ty) =
    fold_rel_context
      (fun (_,copt,_) (largs,subs,ty) ->
        match (copt, largs, ty) with
          | (None, a::args, Prod(_,_,t)) -> (args, a::subs, t)
          | (Some b,_,LetIn(_,_,_,t))    -> (largs, (substl subs b)::subs, t)
	  | (_,[],_)                -> if full then fail() else ([], subs, ty)
	  | _                       -> fail ())
      sign
      ~init:(args,[],t)
  in
  if rem_args <> [] then fail();
  substl subs ty

let instantiate_partial_params = instantiate_params false

let full_inductive_instantiate mib params sign =
  let dummy = Prop Null in
  let t = mkArity (sign,dummy) in
  fst (destArity (instantiate_params true t params mib.mind_params_ctxt))

let full_constructor_instantiate ((mind,_),(mib,_),params) =
  let inst_ind = constructor_instantiate mind mib in
  (fun t ->
    instantiate_params true (inst_ind t) params mib.mind_params_ctxt)

(************************************************************************)
(************************************************************************)

(* Functions to build standard types related to inductive *)


let number_of_inductives mib = Array.length mib.mind_packets
let number_of_constructors mip = Array.length mip.mind_consnames

(*
Computing the actual sort of an applied or partially applied inductive type:

I_i: forall uniformparams:utyps, forall otherparams:otyps, Type(a)
uniformargs : utyps
otherargs : otyps
I_1:forall ...,s_1;...I_n:forall ...,s_n |- sort(C_kj(uniformargs)) = s_kj
s'_k = max(..s_kj..)
merge(..s'_k..) = ..s''_k..
--------------------------------------------------------------------
Gamma |- I_i uniformargs otherargs : phi(s''_i)

where

- if p=0, phi() = Prop
- if p=1, phi(s) = s
- if p<>1, phi(s) = sup(Set,s)

Remark: Set (predicative) is encoded as Type(0)
*)

let sort_as_univ = function
| Type u -> u
| Prop Null -> type0m_univ
| Prop Pos -> type0_univ

let cons_subst u su subst =
  try (u, sup su (List.assoc u subst)) :: List.remove_assoc u subst
  with Not_found -> (u, su) :: subst

let actualize_decl_level env lev t =
  let sign,s = dest_arity env t in
  mkArity (sign,lev)

let polymorphism_on_non_applied_parameters = false

(* Bind expected levels of parameters to actual levels *)
(* Propagate the new levels in the signature *)
let rec make_subst env = function
  | (_,Some _,_ as t)::sign, exp, args ->
      let ctx,subst = make_subst env (sign, exp, args) in
      t::ctx, subst
  | d::sign, None::exp, args ->
      let args = match args with _::args -> args | [] -> [] in
      let ctx,subst = make_subst env (sign, exp, args) in
      d::ctx, subst
  | d::sign, Some u::exp, a::args ->
      (* We recover the level of the argument, but we don't change the *)
      (* level in the corresponding type in the arity; this level in the *)
      (* arity is a global level which, at typing time, will be enforce *)
      (* to be greater than the level of the argument; this is probably *)
      (* a useless extra constraint *)
      let s = sort_as_univ (snd (dest_arity env a)) in
      let ctx,subst = make_subst env (sign, exp, args) in
      d::ctx, cons_subst u s subst
  | (na,None,t as d)::sign, Some u::exp, [] ->
      (* No more argument here: we instantiate the type with a fresh level *)
      (* which is first propagated to the corresponding premise in the arity *)
      (* (actualize_decl_level), then to the conclusion of the arity (via *)
      (* the substitution) *)
      let ctx,subst = make_subst env (sign, exp, []) in
      if polymorphism_on_non_applied_parameters then
	let s = fresh_local_univ () in
	let t = actualize_decl_level env (Type s) t in
	(na,None,t)::ctx, cons_subst u s subst
      else
	d::ctx, subst
  | sign, [], _ ->
      (* Uniform parameters are exhausted *)
      sign,[]
  | [], _, _ ->
      assert false

let instantiate_universes env ctx ar argsorts =
  let args = Array.to_list argsorts in
  let ctx,subst = make_subst env (ctx,ar.poly_param_levels,args) in
  let level = subst_large_constraints subst ar.poly_level in
  ctx,
  if is_type0m_univ level then Prop Null
  else if is_type0_univ level then Prop Pos
  else Type level

let type_of_inductive_knowing_parameters env mip paramtyps =
  match mip.mind_arity with
  | Monomorphic s ->
      s.mind_user_arity
  | Polymorphic ar ->
      let ctx = List.rev mip.mind_arity_ctxt in
      let ctx,s = instantiate_universes env ctx ar paramtyps in
      mkArity (List.rev ctx,s)

(* Type of a (non applied) inductive type *)

let type_of_inductive env (_,mip) =
  type_of_inductive_knowing_parameters env mip [||]

(* The max of an array of universes *)

let cumulate_constructor_univ u = function
  | Prop Null -> u
  | Prop Pos -> sup type0_univ u
  | Type u' -> sup u u'

let max_inductive_sort =
  Array.fold_left cumulate_constructor_univ type0m_univ

(************************************************************************)
(* Type of a constructor *)

let type_of_constructor cstr (mib,mip) =
  let ind = inductive_of_constructor cstr in
  let specif = mip.mind_user_lc in
  let i = index_of_constructor cstr in
  let nconstr = Array.length mip.mind_consnames in
  if i > nconstr then error "Not enough constructors in the type";
  constructor_instantiate (fst ind) mib specif.(i-1)

let arities_of_specif kn (mib,mip) =
  let specif = mip.mind_nf_lc in
  Array.map (constructor_instantiate kn mib) specif



(************************************************************************)

let error_elim_expln kp ki =
  match kp,ki with
  | (InType | InSet), InProp -> NonInformativeToInformative
  | InType, InSet -> StrongEliminationOnNonSmallType (* if Set impredicative *)
  | _ -> WrongArity

(* Type of case predicates *)

(* Get type of inductive, with parameters instantiated *)

let inductive_sort_family mip =
  match mip.mind_arity with
   | Monomorphic s -> family_of_sort s.mind_sort
   | Polymorphic _ -> InType

let mind_arity mip =
  mip.mind_arity_ctxt, inductive_sort_family mip

let get_instantiated_arity (mib,mip) params =
  let sign, s = mind_arity mip in
  full_inductive_instantiate mib params sign, s

let elim_sorts (_,mip) = mip.mind_kelim

let extended_rel_list n hyps =
  let rec reln l p = function
    | (_,None,_) :: hyps -> reln (Rel (n+p) :: l) (p+1) hyps
    | (_,Some _,_) :: hyps -> reln l (p+1) hyps
    | [] -> l
  in
  reln [] 1 hyps

let build_dependent_inductive ind (_,mip) params =
  let realargs,_ = list_chop mip.mind_nrealargs_ctxt mip.mind_arity_ctxt in
  applist
    (Ind ind,
       List.map (lift mip.mind_nrealargs_ctxt) params
       @ extended_rel_list 0 realargs)

(* This exception is local *)
exception LocalArity of (sorts_family * sorts_family * arity_error) option

let check_allowed_sort ksort specif =
  if not (List.exists ((=) ksort) (elim_sorts specif)) then
    let s = inductive_sort_family (snd specif) in
    raise (LocalArity (Some(ksort,s,error_elim_expln ksort s)))

let is_correct_arity env c (p,pj) ind specif params =
  let arsign,_ = get_instantiated_arity specif params in
  let rec srec env pt ar =
    let pt' = whd_betadeltaiota env pt in
    match pt', ar with
      | Prod (na1,a1,t), (_,None,a1')::ar' ->
          (try conv env a1 a1'
          with NotConvertible -> raise (LocalArity None));
          srec (push_rel (na1,None,a1) env) t ar'
      | Prod (_,a1,a2), [] -> (* whnf of t was not needed here! *)
          let ksort = match (whd_betadeltaiota env a2) with
            | Sort s -> family_of_sort s
	    | _ -> raise (LocalArity None) in
	  let dep_ind = build_dependent_inductive ind specif params in
          (try conv env a1 dep_ind
          with NotConvertible -> raise (LocalArity None));
	  check_allowed_sort ksort specif;
	  true
      | Sort s', [] ->
	  check_allowed_sort (family_of_sort s') specif;
	  false
      | _ ->
	  raise (LocalArity None)
  in
  try srec env pj (List.rev arsign)
  with LocalArity kinds ->
    error_elim_arity env ind (elim_sorts specif) c (p,pj) kinds


(************************************************************************)
(* Type of case branches *)

(* [p] is the predicate, [i] is the constructor number (starting from 0),
   and [cty] is the type of the constructor (params not instantiated) *)
let build_branches_type ind (_,mip as specif) params dep p =
  let build_one_branch i cty =
    let typi = full_constructor_instantiate (ind,specif,params) cty in
    let (args,ccl) = decompose_prod_assum typi in
    let nargs = rel_context_length args in
    let (_,allargs) = decompose_app ccl in
    let (lparams,vargs) = list_chop (inductive_params specif) allargs in
    let cargs =
      if dep then
        let cstr = ith_constructor_of_inductive ind (i+1) in
        let dep_cstr =
          applist (Construct cstr,lparams@extended_rel_list 0 args) in
        vargs @ [dep_cstr]
      else
        vargs in
    let base = beta_appvect (lift nargs p) (Array.of_list cargs) in
    it_mkProd_or_LetIn base args in
  Array.mapi build_one_branch mip.mind_nf_lc

(* [p] is the predicate, [c] is the match object, [realargs] is the
   list of real args of the inductive type *)
let build_case_type dep p c realargs =
  let args = if dep then realargs@[c] else realargs in
  beta_appvect p (Array.of_list args)

let type_case_branches env (ind,largs) (p,pj) c =
  let specif = lookup_mind_specif env ind in
  let nparams = inductive_params specif in
  let (params,realargs) = list_chop nparams largs in
  let dep = is_correct_arity env c (p,pj) ind specif params in
  let lc = build_branches_type ind specif params dep p in
  let ty = build_case_type dep p c realargs in
  (lc, ty)


(************************************************************************)
(* Checking the case annotation is relevent *)

let check_case_info env indsp ci =
  let (mib,mip) = lookup_mind_specif env indsp in
  if
    not (eq_ind indsp ci.ci_ind) or
    (mib.mind_nparams <> ci.ci_npar) or
    (mip.mind_consnrealdecls <> ci.ci_cstr_nargs)
  then raise (TypeError(env,WrongCaseInfo(indsp,ci)))

(************************************************************************)
(************************************************************************)

(* Guard conditions for fix and cofix-points *)

(* Check if t is a subterm of Rel n, and gives its specification,
   assuming lst already gives index of
   subterms with corresponding specifications of recursive arguments *)

(* A powerful notion of subterm *)

(* To each inductive definition corresponds an array describing the
   structure of recursive arguments for each constructor, we call it
   the recursive spec of the type (it has type recargs vect).  For
   checking the guard, we start from the decreasing argument (Rel n)
   with its recursive spec.  During checking the guardness condition,
   we collect patterns variables corresponding to subterms of n, each
   of them with its recursive spec.  They are organised in a list lst
   of type (int * recargs) list which is sorted with respect to the
   first argument.
*)

(*************************************************************)
(* Environment annotated with marks on recursive arguments *)

(* tells whether it is a strict or loose subterm *)
type size = Large | Strict

(* merging information *)
let size_glb s1 s2 =
  match s1,s2 with
      Strict, Strict -> Strict
    | _ -> Large

(* possible specifications for a term:
   - Not_subterm: when the size of a term is not related to the
     recursive argument of the fixpoint
   - Subterm: when the term is a subterm of the recursive argument
       the wf_paths argument specifies which subterms are recursive
   - Dead_code: when the term has been built by elimination over an
       empty type
 *)

type subterm_spec =
    Subterm of (size * wf_paths)
  | Dead_code
  | Not_subterm

let spec_of_tree t =
  if Rtree.eq_rtree (=) t mk_norec then Not_subterm else Subterm(Strict,t)

let subterm_spec_glb =
  let glb2 s1 s2 =
    match s1,s2 with
        _, Dead_code -> s1
      | Dead_code, _ -> s2
      | Not_subterm, _ -> Not_subterm
      | _, Not_subterm -> Not_subterm
      | Subterm (a1,t1), Subterm (a2,t2) ->
          if Rtree.eq_rtree (=) t1 t2 then Subterm (size_glb a1 a2, t1)
          (* branches do not return objects with same spec *)
          else Not_subterm in
  Array.fold_left glb2 Dead_code

type guard_env =
  { env     : env;
    (* dB of last fixpoint *)
    rel_min : int;
    (* inductive of recarg of each fixpoint *)
    inds    : inductive array;
    (* the recarg information of inductive family *)
    recvec  : wf_paths array;
    (* dB of variables denoting subterms *)
    genv    : subterm_spec list;
  }

let make_renv env minds recarg (kn,tyi) =
  let mib = lookup_mind kn env in
  let mind_recvec =
    Array.map (fun mip -> mip.mind_recargs) mib.mind_packets in
  { env = env;
    rel_min = recarg+2;
    inds = minds;
    recvec = mind_recvec;
    genv = [Subterm(Large,mind_recvec.(tyi))] }

let push_var renv (x,ty,spec) =
  { renv with
    env = push_rel (x,None,ty) renv.env;
    rel_min = renv.rel_min+1;
    genv = spec:: renv.genv }

let assign_var_spec renv (i,spec) =
  { renv with genv = list_assign renv.genv (i-1) spec }

let push_var_renv renv (x,ty) =
  push_var renv (x,ty,Not_subterm)

(* Fetch recursive information about a variable p *)
let subterm_var p renv =
  try List.nth renv.genv (p-1)
  with Failure _ | Invalid_argument _ -> Not_subterm

(* Add a variable and mark it as strictly smaller with information [spec]. *)
let add_subterm renv (x,a,spec) =
  push_var renv (x,a,spec_of_tree spec)

let push_ctxt_renv renv ctxt =
  let n = rel_context_length ctxt in
  { renv with
    env = push_rel_context ctxt renv.env;
    rel_min = renv.rel_min+n;
    genv = iterate (fun ge -> Not_subterm::ge) n renv.genv }

let push_fix_renv renv (_,v,_ as recdef) =
  let n = Array.length v in
  { renv with
    env = push_rec_types recdef renv.env;
    rel_min = renv.rel_min+n;
    genv = iterate (fun ge -> Not_subterm::ge) n renv.genv }


(******************************)
(* Computing the recursive subterms of a term (propagation of size
   information through Cases). *)

(*
   c is a branch of an inductive definition corresponding to the spec
   lrec.  mind_recvec is the recursive spec of the inductive
   definition of the decreasing argument n.

   case_branches_specif renv lrec lc will pass the lambdas
   of c corresponding to pattern variables and collect possibly new
   subterms variables and returns the bodies of the branches with the
   correct envs and decreasing args.
*)

let lookup_subterms env ind =
  let (_,mip) = lookup_mind_specif env ind in
  mip.mind_recargs

(*********************************)

(* Propagation of size information through Cases: if the matched
   object is a recursive subterm then compute the information
   associated to its own subterms.
   Rq: if branch is not eta-long, then the recursive information
   is not propagated to the missing abstractions *)
let case_branches_specif renv c_spec ind lbr =
  let rec push_branch_args renv lrec c =
    match lrec with
        ra::lr ->
          let c' = whd_betadeltaiota renv.env c in
          (match c' with
              Lambda(x,a,b) ->
                let renv' = push_var renv (x,a,ra) in
                push_branch_args renv' lr b
            | _ -> (* branch not in eta-long form: cannot perform rec. calls *)
                (renv,c'))
      | [] -> (renv, c) in
  match c_spec with
      Subterm (_,t) ->
        let sub_spec = Array.map (List.map spec_of_tree) (dest_subterms t) in
        assert (Array.length sub_spec = Array.length lbr);
        array_map2 (push_branch_args renv) sub_spec lbr
    | Dead_code ->
        let t = dest_subterms (lookup_subterms renv.env ind) in
        let sub_spec = Array.map (List.map (fun _ -> Dead_code)) t in
        assert (Array.length sub_spec = Array.length lbr);
        array_map2 (push_branch_args renv) sub_spec lbr
    | Not_subterm -> Array.map (fun c -> (renv,c)) lbr

(* [subterm_specif renv t] computes the recursive structure of [t] and
   compare its size with the size of the initial recursive argument of
   the fixpoint we are checking. [renv] collects such information
   about variables.
*)

let rec subterm_specif renv t =
  (* maybe reduction is not always necessary! *)
  let f,l = decompose_app (whd_betadeltaiota renv.env t) in
  match f with
    | Rel k -> subterm_var k renv

    | Case (ci,_,c,lbr) ->
        if Array.length lbr = 0 then Dead_code
        else
          let c_spec = subterm_specif renv c in
          let lbr_spec = case_branches_specif renv c_spec ci.ci_ind lbr in
          let stl  =
            Array.map (fun (renv',br') -> subterm_specif renv' br')
              lbr_spec in
          subterm_spec_glb stl

    | Fix ((recindxs,i),(_,typarray,bodies as recdef)) ->
(* when proving that the fixpoint f(x)=e is less than n, it is enough
   to prove that e is less than n assuming f is less than n
   furthermore when f is applied to a term which is strictly less than
   n, one may assume that x itself is strictly less than n
*)
        let (ctxt,clfix) = dest_prod renv.env typarray.(i) in
        let oind =
          let env' = push_rel_context ctxt renv.env in
          try Some(fst(find_inductive env' clfix))
          with Not_found -> None in
        (match oind with
            None -> Not_subterm (* happens if fix is polymorphic *)
          | Some ind ->
              let nbfix = Array.length typarray in
              let recargs = lookup_subterms renv.env ind in
              (* pushing the fixpoints *)
              let renv' = push_fix_renv renv recdef in
              let renv' =
                (* Why Strict here ? To be general, it could also be
                   Large... *)
                assign_var_spec renv' (nbfix-i, Subterm(Strict,recargs)) in
              let decrArg = recindxs.(i) in
              let theBody = bodies.(i)   in
              let nbOfAbst = decrArg+1 in
              let sign,strippedBody = decompose_lam_n_assum nbOfAbst theBody in
              (* pushing the fix parameters *)
              let renv'' = push_ctxt_renv renv' sign in
              let renv'' =
                if List.length l < nbOfAbst then renv''
                else
                  let theDecrArg  = List.nth l decrArg in
	          let arg_spec    = subterm_specif renv theDecrArg in
                  assign_var_spec renv'' (1, arg_spec) in
	      subterm_specif renv'' strippedBody)

    | Lambda (x,a,b) ->
        assert (l=[]);
        subterm_specif (push_var_renv renv (x,a)) b

    (* Metas and evars are considered OK *)
    | (Meta _|Evar _) -> Dead_code

    (* Other terms are not subterms *)
    | _ -> Not_subterm


(* Check term c can be applied to one of the mutual fixpoints. *)
let check_is_subterm renv c =
  match subterm_specif renv c with
    Subterm (Strict,_) | Dead_code -> true
  |  _ -> false

(************************************************************************)

exception FixGuardError of env * guard_error

let error_illegal_rec_call renv fx arg =
  let (_,le_vars,lt_vars) =
    List.fold_left
      (fun (i,le,lt) sbt ->
        match sbt with
            (Subterm(Strict,_) | Dead_code) -> (i+1, le, i::lt)
          | (Subterm(Large,_)) -> (i+1, i::le, lt)
          | _ -> (i+1, le ,lt))
      (1,[],[]) renv.genv in
  raise (FixGuardError (renv.env,
                        RecursionOnIllegalTerm(fx,arg,le_vars,lt_vars)))

let error_partial_apply renv fx =
  raise (FixGuardError (renv.env,NotEnoughArgumentsForFixCall fx))

(* Check if [def] is a guarded fixpoint body with decreasing arg.
   given [recpos], the decreasing arguments of each mutually defined
   fixpoint. *)
let check_one_fix renv recpos def =
  let nfi = Array.length recpos in

  (* Checks if [t] only make valid recursive calls *)
  let rec check_rec_call renv t =
    (* if [t] does not make recursive calls, it is guarded: *)
    if noccur_with_meta renv.rel_min nfi t then ()
    else
      let (f,l) = decompose_app (whd_betaiotazeta renv.env t) in
      match f with
        | Rel p ->
            (* Test if [p] is a fixpoint (recursive call) *)
	    if renv.rel_min <= p & p < renv.rel_min+nfi then
              begin
                List.iter (check_rec_call renv) l;
                (* the position of the invoked fixpoint: *)
	        let glob = renv.rel_min+nfi-1-p in
                (* the decreasing arg of the rec call: *)
	        let np = recpos.(glob) in
                if List.length l <= np then error_partial_apply renv glob
                else
                  (* Check the decreasing arg is smaller *)
                  let z = List.nth l np in
	          if not (check_is_subterm renv z) then
                    error_illegal_rec_call renv glob z
              end
            else
              begin
                match pi2 (lookup_rel p renv.env) with
                | None ->
                    List.iter (check_rec_call renv) l
                | Some c ->
                    try List.iter (check_rec_call renv) l
                    with FixGuardError _ -> check_rec_call renv (applist(c,l))
              end

        | Case (ci,p,c_0,lrest) ->
            List.iter (check_rec_call renv) (c_0::p::l);
            (* compute the recarg information for the arguments of
               each branch *)
            let c_spec = subterm_specif renv c_0 in
            let lbr = case_branches_specif renv c_spec ci.ci_ind lrest in
            Array.iter (fun (renv',br') -> check_rec_call renv' br') lbr

        (* Enables to traverse Fixpoint definitions in a more intelligent
           way, ie, the rule :
           if - g = Fix g/p := [y1:T1]...[yp:Tp]e &
              - f is guarded with respect to the set of pattern variables S
                in a1 ... am        &
              - f is guarded with respect to the set of pattern variables S
                in T1 ... Tp        &
              - ap is a sub-term of the formal argument of f &
              - f is guarded with respect to the set of pattern variables
                S+{yp} in e
           then f is guarded with respect to S in (g a1 ... am).
           Eduardo 7/9/98 *)

        | Fix ((recindxs,i),(_,typarray,bodies as recdef)) ->
            List.iter (check_rec_call renv) l;
            Array.iter (check_rec_call renv) typarray;
            let decrArg = recindxs.(i) in
            let renv' = push_fix_renv renv recdef in
            if (List.length l < (decrArg+1)) then
	      Array.iter (check_rec_call renv') bodies
            else
              Array.iteri
                (fun j body ->
                  if i=j then
                    let theDecrArg  = List.nth l decrArg in
	            let arg_spec = subterm_specif renv theDecrArg in
	            check_nested_fix_body renv' (decrArg+1) arg_spec body
                  else check_rec_call renv' body)
                bodies

        | Const kn ->
            if evaluable_constant kn renv.env then
              try List.iter (check_rec_call renv) l
              with (FixGuardError _ ) ->
	        check_rec_call renv(applist(constant_value renv.env kn, l))
	    else List.iter (check_rec_call renv) l

        (* The cases below simply check recursively the condition on the
           subterms *)
        | Cast (a,_, b) ->
            List.iter (check_rec_call renv) (a::b::l)

        | Lambda (x,a,b) ->
            List.iter (check_rec_call renv) (a::l);
            check_rec_call (push_var_renv renv (x,a)) b

        | Prod (x,a,b) ->
            List.iter (check_rec_call renv) (a::l);
            check_rec_call (push_var_renv renv (x,a)) b

        | CoFix (i,(_,typarray,bodies as recdef)) ->
            List.iter (check_rec_call renv) l;
	    Array.iter (check_rec_call renv) typarray;
	    let renv' = push_fix_renv renv recdef in
	    Array.iter (check_rec_call renv') bodies

        | (Ind _ | Construct _ | Sort _) ->
            List.iter (check_rec_call renv) l

        | Var id ->
            begin
              match pi2 (lookup_named id renv.env) with
              | None ->
                  List.iter (check_rec_call renv) l
              | Some c ->
                  try List.iter (check_rec_call renv) l
                  with (FixGuardError _) -> check_rec_call renv (applist(c,l))
            end

        (* l is not checked because it is considered as the meta's context *)
        | (Evar _ | Meta _) -> ()

        | (App _|LetIn _) -> assert false (* beta zeta reduction *)

  and check_nested_fix_body renv decr recArgsDecrArg body =
    if decr = 0 then
      check_rec_call (assign_var_spec renv (1,recArgsDecrArg)) body
    else
      match body with
	| Lambda (x,a,b) ->
	    check_rec_call renv a;
            let renv' = push_var_renv renv (x,a) in
	    check_nested_fix_body renv' (decr-1) recArgsDecrArg b
	| _ -> anomaly "Not enough abstractions in fix body"

  in
  check_rec_call renv def


let inductive_of_mutfix env ((nvect,bodynum),(names,types,bodies as recdef)) =
  let nbfix = Array.length bodies in
  if nbfix = 0
    or Array.length nvect <> nbfix
    or Array.length types <> nbfix
    or Array.length names <> nbfix
    or bodynum < 0
    or bodynum >= nbfix
  then anomaly "Ill-formed fix term";
  let fixenv = push_rec_types recdef env in
  let raise_err env i err =
    error_ill_formed_rec_body env err names i in
  (* Check the i-th definition with recarg k *)
  let find_ind i k def =
    (* check fi does not appear in the k+1 first abstractions,
       gives the type of the k+1-eme abstraction (must be an inductive)  *)
    let rec check_occur env n def =
      match (whd_betadeltaiota env def) with
        | Lambda (x,a,b) ->
	    if noccur_with_meta n nbfix a then
	      let env' = push_rel (x, None, a) env in
              if n = k+1 then
                (* get the inductive type of the fixpoint *)
                let (mind, _) =
                  try find_inductive env a
                  with Not_found ->
		    raise_err env i (RecursionNotOnInductiveType a) in
                (mind, (env', b))
	      else check_occur env' (n+1) b
            else anomaly "check_one_fix: Bad occurrence of recursive call"
        | _ -> raise_err env i NotEnoughAbstractionInFixBody in
    check_occur fixenv 1 def in
  (* Do it on every fixpoint *)
  let rv = array_map2_i find_ind nvect bodies in
  (Array.map fst rv, Array.map snd rv)


let check_fix env ((nvect,_),(names,_,bodies as _recdef) as fix) =
  let (minds, rdef) = inductive_of_mutfix env fix in
  for i = 0 to Array.length bodies - 1 do
    let (fenv,body) = rdef.(i) in
    let renv = make_renv fenv minds nvect.(i) minds.(i) in
    try check_one_fix renv nvect body
    with FixGuardError (fixenv,err) ->
      error_ill_formed_rec_body fixenv err names i
  done

(*
let cfkey = Profile.declare_profile "check_fix";;
let check_fix env fix = Profile.profile3 cfkey check_fix env fix;;
*)

(************************************************************************)
(* Co-fixpoints. *)

exception CoFixGuardError of env * guard_error

let anomaly_ill_typed () =
  anomaly "check_one_cofix: too many arguments applied to constructor"

let rec codomain_is_coind env c =
  let b = whd_betadeltaiota env c in
  match b with
    | Prod (x,a,b) ->
	codomain_is_coind (push_rel (x, None, a) env) b
    | _ ->
	(try find_coinductive env b
        with Not_found ->
	  raise (CoFixGuardError (env, CodomainNotInductiveType b)))

let check_one_cofix env nbfix def deftype =
  let rec check_rec_call env alreadygrd n vlra  t =
    if not (noccur_with_meta n nbfix t) then
      let c,args = decompose_app (whd_betadeltaiota env t) in
      match c with
	| Rel p when  n <= p && p < n+nbfix ->
	    (* recursive call: must be guarded and no nested recursive
               call allowed *)
            if not alreadygrd then
	      raise (CoFixGuardError (env,UnguardedRecursiveCall t))
            else if not(List.for_all (noccur_with_meta n nbfix) args) then
	      raise (CoFixGuardError (env,NestedRecursiveOccurrences))

	| Construct (_,i as cstr_kn)  ->
            let lra = vlra.(i-1) in
            let mI = inductive_of_constructor cstr_kn in
	    let (mib,mip) = lookup_mind_specif env mI in
            let realargs = list_skipn mib.mind_nparams args in
            let rec process_args_of_constr = function
              | (t::lr), (rar::lrar) ->
                  if rar = mk_norec then
                    if noccur_with_meta n nbfix t
                    then process_args_of_constr (lr, lrar)
                    else raise (CoFixGuardError
		                 (env,RecCallInNonRecArgOfConstructor t))
                  else
                    let spec = dest_subterms rar in
                    check_rec_call env true n spec t;
                    process_args_of_constr (lr, lrar)
              | [],_ -> ()
              | _ -> anomaly_ill_typed ()
            in process_args_of_constr (realargs, lra)

	| Lambda (x,a,b) ->
	     assert (args = []);
            if noccur_with_meta n nbfix a then
              let env' = push_rel (x, None, a) env in
              check_rec_call env' alreadygrd (n+1)  vlra b
            else
	      raise (CoFixGuardError (env,RecCallInTypeOfAbstraction a))

	| CoFix (j,(_,varit,vdefs as recdef)) ->
            if (List.for_all (noccur_with_meta n nbfix) args)
            then
              let nbfix = Array.length vdefs in
	      if (array_for_all (noccur_with_meta n nbfix) varit) then
		let env' = push_rec_types recdef env in
		(Array.iter (check_rec_call env' alreadygrd (n+1) vlra) vdefs;
		 List.iter (check_rec_call env alreadygrd n vlra) args)
              else
		raise (CoFixGuardError (env,RecCallInTypeOfDef c))
	    else
	      raise (CoFixGuardError (env,UnguardedRecursiveCall c))

	| Case (_,p,tm,vrest) ->
            if (noccur_with_meta n nbfix p) then
              if (noccur_with_meta n nbfix tm) then
		if (List.for_all (noccur_with_meta n nbfix) args) then
		  Array.iter (check_rec_call env alreadygrd n vlra) vrest
		else
		  raise (CoFixGuardError (env,RecCallInCaseFun c))
              else
		raise (CoFixGuardError (env,RecCallInCaseArg c))
            else
	      raise (CoFixGuardError (env,RecCallInCasePred c))

	| Meta _ -> ()
        | Evar _ ->
	    List.iter (check_rec_call env alreadygrd n vlra) args

	| _    -> raise (CoFixGuardError (env,NotGuardedForm t)) in

  let (mind, _) = codomain_is_coind env deftype in
  let vlra = lookup_subterms env mind in
  check_rec_call env false 1 (dest_subterms vlra) def

(* The  function which checks that the whole block of definitions
   satisfies the guarded condition *)

let check_cofix env (bodynum,(names,types,bodies as recdef)) =
  let nbfix = Array.length bodies in
  for i = 0 to nbfix-1 do
    let fixenv = push_rec_types recdef env in
    try check_one_cofix fixenv nbfix bodies.(i) types.(i)
    with CoFixGuardError (errenv,err) ->
      error_ill_formed_rec_body errenv err names i
  done